1. Field of the Invention
The present invention relates to a drive circuit fault detection device, in particular, for output short circuiting or disconnected load detection.
2. Discussion of the Related Art
In the following description, reference will be made to a so-called low-side-driver circuit, i.e. wherein the drive circuit is grounded and the load connected to a positive supply, thus requiring detection of ground shorting of the circuit output. The present invention, however, is equally applicable to so-called high-side-driver circuits.
FIG. 1 shows the overall structure of a prior art low-side-driver circuit, wherein drive circuit 1 is shown schematically by its control element, including a power transistor 2 having a first (control) terminal 3 receiving a control signal (IN); a second terminal 4 connected to positive supply line V.sub.CC via load 5; and a third terminal 6 grounded via resistor 7. Terminal 4 of transistor 2 also supplies the drive circuit output.
In the above known circuit, ground shorting of output 4, as shown schematically by dotted line 8, is detected by monitoring the current in the control element, normally by means of a sensing resistor frequently implemented by resistor 7 itself, shorting being indicated by failure of said current to reach a given value within a given length of time.
A major drawback of the above known solution is that it entails defining beforehand a short-circuit resistance which, to ensure correct detection, must be considerably less than the equivalent resistance of control element 2.
It is an object of the present invention to provide a fault (specifically, ground shorting) detection device, which, by virtue of not requiring a predefined short-circuit resistance, does not entail detecting or monitoring the current in the control element.